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Evidence for presence and hormonal regulation of protein phosphatase inhibitor-1 in ventricular cardiomyocyte
Ist Teil von
American journal of physiology. Heart and circulatory physiology, 1996-04, Vol.270 (4), p.H1159-H1164
Ort / Verlag
United States
Erscheinungsjahr
1996
Link zum Volltext
Quelle
MEDLINE
Beschreibungen/Notizen
R. C. Gupta, J. Neumann, A. M. Watanabe, M. Lesch and H. N. Sabbah
Department of Medicine, Henry Ford Heart and Vascular Institute, Henry Ford Hospital, Detroit, Michigan 48202, USA.
Protein phosphatase inhibitor-1 (PPI-1) has been shown to be present in
heart tissue and smooth muscle. Whether PPI-1 is present in cardiomyocytes
is not known. The purpose of this study was to determine whether PPI-1 is
present and is hormonally regulated in cardiomyocytes. A trichloroacetic
acid (TCA) extract enriched in PPI-1 was isolated from guinea pig
ventricular cardiomyocytes. The TCA extract inhibited the activity of type
1 protein phosphatase by 20 +/- 4% (n = 3 expts). On phosphorylation by the
catalytic subunit of adenosine 3', 5'-cyclic monophosphate-dependent
protein kinase, the extent of this inhibition was augmented to 4.5-fold.
Dephosphorylation of the phosphorylated TCA extract by type 2 protein
phosphatase reduced inhibition to 2 +/- 0.2% (n = 3 expts). To determine
whether isoproterenol increases phosphorylation of PPI-1 in cardiomyocytes,
the TCA extracts were prepared from cardiomyocytes treated with 1 microM
isoproterenol and from untreated cardiomyocytes. The inhibitory activity of
the TCA extract in untreated cardiomyocytes was 25 +/- 3% (n = 3 expts) and
increased to 75 +/- 2% (n = 3 expts) in isoproterenol-treated
cardiomyocytes. With the use of a rabbit skeletal muscle PPI-1 antibody,
immunoblots of the TCA extract of cardiomyocytes identified a 28-kDa
protein. A 28-kDa protein was also immunoprecipitated from a TCA extract
isolated from isoproterenol-treated 32P-labeled cardiomyocytes. The
immunoprecipitation was blocked by the addition of excess amounts of
purified rabbit skeletal muscle PPI-1. Isoproterenol-treated cardiomyocytes
increased the phosphorylation of the 28-kDa protein by 232 +/- 20% (n = 3
expts) compared with untreated cardiomyocytes. We conclude that 1) the
28-kDa protein is PPI-1, 2) PPI-1 is present in ventricular cardiomyocytes,
and 3) PPI-1 is hormonally regulated. A decrease in type 1 protein
phosphatase activity through phosphorylation of PPI-1 may be an important
pathway for augmenting cardiac contractility.